Design Of Pattern Diversity Antennas And Pattern Reconfigurable Antennas

The mobile terminal devices are becoming more and more compact and integrated.Therefore,it is more difficult to increase the number of antennas on a single device.Unlike array antennas,pattern diversity antennas(PDAs)and pattern reconfigurable antennas(PRAs)have the advantages of compact size,low cost,and the ability to change the radiation patterns without complex feed network.As a result,PDAs and PRAs have been widely concerned and studied by scholars at home and abroad.Closly related to the research topics,metasurface(MTS)-based PDA and the microstrip patch-based E-plane beamwidth reconfigurable antenna are designed and studied in depth.The main research results of this thesis can be summarized as follows:1.A low-profile wideband PDA based on MTS is proposed.Initially,based on the theory of characteristic mode(TCM),the diversity characteristic of broadside and conical radiation pattern is realized by selectively exciting two characteristic modes of the metasurface with relatively close resonant frequencies.Then,by analyzing the modal current distribution on the MTS,the optimal relative phases of the four feeding patches are set up to excite the above two modes.However,the in-band high-order modes(HOMs)introduced by the feeding structure will deteriorate the radiation pattern.Therefore,by tracing the modes and analyzing the modal current distribution on MTS,the structures of the feeding patches and the MTS are improved to suppress the in-band HOMs for improvement of radiation pattern.Finally,the antenna is fabricated and measured.The test results show that the proposed antenna has extremely low profile of 0.06?₀(?₀ refers to the free-space wavelength at the center frequency)and an isolation of better than 38 dB,which also maintains an operating bandwidth of 20.24%.Based on these excellent performances,the proposed antenna is an attractive solution for pattern diversity applications requiring low profile.2.A microstrip-based E-plane beamwidth reconfigurable antenna is designed.By controlling several PIN diodes to reconfigure the position of the radiation slots of the microstrip antenna,the E-plane pattern can be switched between wide beam and narrow beam.Through theoretical analysis of traditional microstrip antennas and utilization of short-circuit loading and RF switches loading,the distance between the two radiation slots of the microstrip antenna can be swiched between the short distance and the long distance,and the designed antenna can obtain the reconfigurable ability of the E-plane pattern.The antenna is simulated and tested,and the tested results show that the E-plane beam width of the antenna can achieve two states of 149.6°and 52.7°.The overlapped bandwidth of the two states is 5.2%(2.80?2.95 GHz).The gain in the main radiation direction is-3.53?-1.38 dBi under the wide beam state of the E plane,and7.04?7.54 dBi under the narrow beam state of the E plane.